1. Field of the Invention
The present invention relates to a packet transmission method in which packets are transmitted between a base station and a mobile station communicating with the base station when the packets are transmitted from a sender to a receiver, and to a base station and a mobile station to which the packet transmission method is applied.
2. Description of the Related Art
As multimedia service makes progress in these years, in addition to the conventional voice communication, non-voice communication such as image communication is being performed. In many cases, the size of each packet transmitted in the non-voice communication differs depending on an application used for processing the packet and the type of the packet (for example, types such as a control packet, an information packet, and the like). More specifically, the size of a packet varies widely from several bytes of the control packet to 1500 bytes prescribed by MTU.
As mentioned above, various sizes of packets are transmitted. However, there is a demand for reducing variation of packet transmission time when transmitting packets each having a different size from a sender to a receiver.
For example, take a case where moving image data transmitted from a sender are reproduced by a receiver by streaming playback. in this case, the size of a packet including the moving image data varies according to variations of the images. However, it is necessary to reduce variation of packet transmission time when transmitting packets each having a different size in order to smoothly reproduce the moving image data at the receiver.
In addition, conventionally, in a system where a sender and a receiver communicate each other through a plurality of networks, there is a demand for satisfying transmission quality from the sender to the receiver, that is, end-to-end transmission quality.
However, conventionally, it is difficult to reduce variation of packet transmission time when transmitting packets each having a different size from a sender to a receiver.
For example, in Japanese Laid-Open Patent Application No. 2001-016276 “Communication Equipment, Communication Method, Storage Medium and Communication System”, a method is proposed in which packets in a buffer holding a small amount of data are transmitted at low speed, while packets in a buffer holding a large amount of data are transmitted at high speed so as to make the transmission rate variable. In other words, transmission time in transmitting packets is adjusted.
However, in a case where packets having large sizes are held in a buffer holding a small amount of data, the packets thereof are transmitted at low speed. On the other hand, in a case where packets having small sizes are held in a buffer holding a large amount of data, the packets thereof are transmitted at high speed. Accordingly, variation of packet transmission time becomes greater.
Additionally, conventionally, in a system communicating with a plurality of networks, a transmission rate is determined for each of the networks according to a predetermined priority. Thus, in many cases, transmission quality is not satisfied even when it is required to satisfy transmission quality from a sender to a receiver, that is, end-to-end transmission quality.